Édouard Stephan discovered NGC 6042 = St I-3, along with NGC 6040 and NGC 6041, on 27 Jun 1870. His position is accurate.

300/350mm - 13.1" (6/29/84): extremely faint, at visual threshold, very small, round.

400/500mm - 17.5" (5/13/88): very faint, very small, round. Third of three NGC galaxies on a line with NGC 6041 1.5' NW and NGC 6040 4.3' NW in the core of AGC 2151. Also extremely faint IC 1170 lies 2.3' NW. Located 1.7' NE of a mag 11 star.

17.5" (3/23/85): faint, very small, roundish. Faintest in trio on a line in AGC 2151.

Notes by Steve Gottlieb